Bob Riha, Jr./Getty Images(LOS ANGELES) — Kelsey Grammer is mourning the loss of John Mahoney, who played his dad for 11 seasons on the hit sitcom Frasier.

On Wednesday, Grammer tweeted a black-and-white photo of him and Mahoney embracing.

“He was my father,” Grammer wrote. “I loved him.”

Mahoney passed away Sunday in Chicago, Illinois. He was 77.

On Frasier, the late actor played Martin Crane, the grouchy but lovable former cop father to Grammer’s Frasier and David Hyde Pierce’s Niles. Mahoney, a stage and screen veteran, was nominated for two Emmys for the role.